Reduction drives

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TFF

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The overrunning clutch is tuned by design to stay engaged just a little more of the amount of inertia decay of normal throttle changes. Abrupt or total loss will disengage, but normal flight throttling does not. Flat pitch rotors retains a lot of inertia, but with with flight , there is a lot of drag on the blades because the angles of attack to fly and maneuver. That keeps the engine and blades married. That’s the problem with low inertia blade systems used on R22s and homebuilt helicopters. The drag is way higher than the inertia, and they will decay so fast with out action that they are essentially stopped because they are out of useful rpm. Flat pitch you can split the engine and blades easily. Once flying, the blades are trying to stop everything from turning and only the engine pushing the blades spinning is keeping it in the air. One to two seconds is the reaction time to get in autorotation mode or you may be in trouble. That’s a lot of drag over inertia.
 

wsimpso1

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Thanks for the tip on SDSEFT.com I was suggesting that more inertia be added to the engine side, since the rotary engine is so small
Tracy Crook's RWS seems to work. I would consider his system the default. Check out the Inertia of his systems as flown, and then Deviate from it only for really good reason. The biggest difference I would be concerned over is props. Check out the props on successful RWS installs - you would need to be in that neighborhood with your prop install. After a careful determination of Inertia on both sides and then of the natural frequencies of the system, only then would I start thinking about moving away from the developed and demonstrated system.

Billski
 

wsimpso1

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If I recall correctly the Ross used a Ford C6 planet set and the GAP used a Ford E4OD planet set.
The E4OD, 4R100, 5R100, and 5R110 were all C6's with an overdrive and a converter clutch. MANY C6 part numbers lived on through the end of 5R110 production in 2009. The planetaries were upgraded repeatedly over the 40+ years of production, both in Ford production and in aftermarket pieces. It is possible that the Ross units had less pinions and other upgrades, while later ones had more. Tranny product engineer at Ford for 18 years...

IThe problem that I was never able to overcome was planet bearing failure. The tiny needle bearings in the planet gears would start to fail after about 20 hours (see photo). Calculated rotational speed of the needles at cruise speed comes to over 100K RPM. I came to the conclusion that the Ford planetaries were designed for about a 10% duty cycle. I have been told that rotary and smaller piston conversions have had better results with planetary drives.
Not surprising. Automotive planetaries use helical gears for quietness, which adds an overturning moment to the planet gear. This tends to edge load the needles at one edge on one end and on the opposite end on the other side. Straight teeth would solve this, but I do not recall any aftermarket racing planet sets like this.

In cars and trucks, these planetary sets do pass huge long very high power tests, including high power sustained operations and field problems were non-existent. The usual reasons for planetary replacements in the field were 300,000 miles and/or failed clutch pieces going through the mesh. In drag racers, running north of 800 ft-lb, they also tend to have short lives, but so do many of the other internal parts.

My suspicion is that the issue in your airplane is the same as in others of similar design - inadequate isolation of firing pulses. At some point in the operating range, firing pulses are near resonance, which loads and unloads the gears, with impact, and that will quickly build up this sort of wear. In cars and trucks, firing (and other orders) vibration is well isolated from the rest of the powertrain - unloading does not happen inside the gearboxes...

I have since installed a Marcotte drive with internal spur gears and have been getting better results.
Russell Sherwood - Glasair IRG/Subaru EG33
The Marcotte looks like excellent kit.

Bill
 

wsimpso1

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It's been a long time since I have looked at Tracy's whole package. I didn't recall that it had a damper. Thank you for the heads up.
He has a damper, it was pictured in post 139. The soft elements are molded elastomer bushings in the corners of the plate.

Bill
 

BBerson

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The piston helicopters have a belt tightener like a lawn mower to disengage and get it started and up to speed by slipping the belt. They don't use cogged belts. I think the multiple V or 7" micro V on the Enstrom is the way to go.
 

cheapracer

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The overrunning clutch is tuned by design to stay engaged just a little more of the amount of inertia decay of normal throttle changes. Abrupt or total loss will disengage, but normal flight throttling does not. Flat pitch rotors retains a lot of inertia, but with with flight , there is a lot of drag on the blades because the angles of attack to fly and maneuver. That keeps the engine and blades married. That’s the problem with low inertia blade systems used on R22s and homebuilt helicopters. The drag is way higher than the inertia, and they will decay so fast with out action that they are essentially stopped because they are out of useful rpm. Flat pitch you can split the engine and blades easily. Once flying, the blades are trying to stop everything from turning and only the engine pushing the blades spinning is keeping it in the air. One to two seconds is the reaction time to get in autorotation mode or you may be in trouble. That’s a lot of drag over inertia.
Deserves a simple reply: 'Brilliant explaination'

Completely opposite to what I had thought, love this forum some days, thanks.
 

cheapracer

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The piston helicopters have a belt tightener like a lawn mower to disengage and get it started and up to speed by slipping the belt. They don't use cogged belts. I think the multiple V or 7" micro V on the Enstrom is the way to go.
Yes, aware, thanks.

I have actually built a couple of karts for my kids back when, with 'belt take up clutch' drive.

Plenty of industrial machines around with the same setup too.
 

wsimpso1

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Thanks for the tip on SDSEFT.com I was suggesting that more inertia be added to the engine side, since the rotary engine is so small
I understood your suggestion, and my comments are unchanged. Seriously, I would not deviate from RWS without some really thorough analysis and a shortcoming that must be corrected in order to make it reliable.

Elsewhere on this forum I have become known for strongly making the case for people to select known good airplanes and stick to the plans. The exception to sticking to the plans is when there is a known fix for a known flaw, and then stick to the plans for the known fix. Doing anything else is taking on the task of airplane designer (or in this case, powerplant designer), experimental fabricator, and test pilot for a new airplane (or powerplant).

Billski
 

Bill-Higdon

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The overrunning clutch is tuned by design to stay engaged just a little more of the amount of inertia decay of normal throttle changes. Abrupt or total loss will disengage, but normal flight throttling does not. Flat pitch rotors retains a lot of inertia, but with with flight , there is a lot of drag on the blades because the angles of attack to fly and maneuver. That keeps the engine and blades married. That’s the problem with low inertia blade systems used on R22s and homebuilt helicopters. The drag is way higher than the inertia, and they will decay so fast with out action that they are essentially stopped because they are out of useful rpm. Flat pitch you can split the engine and blades easily. Once flying, the blades are trying to stop everything from turning and only the engine pushing the blades spinning is keeping it in the air. One to two seconds is the reaction time to get in autorotation mode or you may be in trouble. That’s a lot of drag over inertia.
The Army on the TH-55's emphasized bottom the collective immediately if you had to do a auto rotation, of course you were flying "low" at that time and not at a more normal civilian training altitude
 

wsimpso1

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Why hasn't anyone used a Robbo R22 dual V belt and sheave reduction? Proven, been around a long time etc.
They work. The system has zero lash on the engine side of the soft element. Helo systems have MMOI orders of magnitude larger than a prop. Add in the belts and the long shaft between upper sheave and rotor gearbox, you have a BIG inertia separated from the engine by a soft element. I would bet that the first resonant order of the system is down around engine starting rpm. While that nicely isolates firing and other engine vibe orders from the gearbox and rotor, it does mean that you have to go through that vibration on start up and shut down. That is where the OWC comes into play. As you go through resonance, the OWC carries torque in the positive torque direction, and unloads as the engine slows between firing pulses, forestalling the amplification that constitutes resonance. Once you get into operating speeds, the firing pulses occur much closer together (in time), the amplitude of the various shaft speed and angular swings becomes much smaller, and only the elasticity of the system parts is cycling over the train of firing pulses - the OWC only unloads around resonance or if the engine falls off line.

They are kind of heavy and bulky, which probably accounts for no one seeing a market for one in airplanes.

Curiously, Lockheed built a stealthy airplane for reconnaissance during the Vietnam war, with a muti-belt drive and layshaft to reduce propellor rpm for quietness. Worked great.

Billski
 

wsimpso1

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The helicopter has a big overrunning clutch in the upper sheave (or lower?) which can cancel half the torsional vibration forcing from the rotor in theory. I don't know if it does in practice.
My bet is they go through resonance well below idle, most likely during start up and shut down. The OWC then does keep the system from tearing itself apart until it gets to idle or above.
 

pictsidhe

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The Crook RWS is known to work very well. Change anything at your own peril. I am attempting to design my own redrive, getting one to work well is a lot harder than it looks.

Ross (rv6ejguy) flies a Marcotte.
 

rv7charlie

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snipped

Curiously, Lockheed built a stealthy airplane for reconnaissance during the Vietnam war, with a muti-belt drive and layshaft to reduce propellor rpm for quietness. Worked great.

Billski
Even more curiously ( :) ), early versions of this almost silent a/c were powered by a Wankel rotary engine.
http://all-aero.com/index.php/53-planes-l-m-n-o/6207-lockheed-qt-2--q-star
One of the members on the Flyrotary email list is restoring one of the original rotary powered a/c. He gave a detailed presentation on it at one of our 'Rotary Roundups' several years ago. I've got a copy of his presentation somewhere, but I can't locate it at the moment.

Charlie
 

cheapracer

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Curiously, Lockheed built a stealthy airplane for reconnaissance during the Vietnam war, with a muti-belt drive and layshaft to reduce propellor rpm for quietness. Worked great.
I have read about it before, the one with the funny overhead driveshaft/rear engine/forward prop, but didn't know it was belt driven, off to find more info on that drive then ...

Oh RVcharlie has pinpoited the model.
 

TFF

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To above, of course you bottom the collective!

Lot flying fat dumb and happy are not thinking this. One of my old pilots who is very good actually was stuck doing a night transition flight, piston helicopter. About an hour and a half into it and the engine lost a cylinder. It coughed and for a second it stopped running. The pilot with his log legs had his feet stretched out not on the pedals. He pulled his feet back so hard he ripped the skid plate on the floor. I’m sure his had was not on the collective. Collective down. His bad reaction time is probably better than my good one but it happens when you are not ready, not when you are. If he was in a robby he would have been sweating a lot more. He saw engine was running and powered up. We thought it might had swallowed some water. Zero compression on #3. It was so dead I had to check myself if I was doing the compression check right. There is a lot of drag on those blades. Wait 10 seconds and you have in recoverable blade stall. Helicopter will eat it’s self.
 

wsimpso1

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Even more curiously ( :) ), early versions of this almost silent a/c were powered by a Wankel rotary engine.
http://all-aero.com/index.php/53-planes-l-m-n-o/6207-lockheed-qt-2--q-star
One of the members on the Flyrotary email list is restoring one of the original rotary powered a/c. He gave a detailed presentation on it at one of our 'Rotary Roundups' several years ago. I've got a copy of his presentation somewhere, but I can't locate it at the moment.

Charlie
News to me. I was writing about the Lockheed YO-3. There was more than one type built.
 

Vigilant1

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I thought it was interesting to read that they experimented with the Wankel because of the noise from the valves on the piston engine. When the valve noise is noticeable, you've got a very quiet exhaust system and prop.
I know a guy who served in a long-range recce capacity in that conflict, but not in uniform and not in North or South Vietnam. He had a lot of good things to say about this program and the guys who served as pilots and observers on those planes.
 
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